This invention relates to optical indicia readers, such as bar code readers, and is directed more particularly to optical indicia readers having illumination optics assemblies that include improved aiming illumination pattern generators.
Bar code readers have, until recently, been designed to scan linearly in one dimension only. As disclosed in U.S. Pat. Nos. 5,378,883 to Batterman and 5,331,786 to Sant Anselmo et al. "omnidirectional" readers have been developed that utilize solid state imagers that are able to scan rapidly in two dimensions. The 2D readers also have the ability of reading multiple targets during the course of one scanning pass to acquire additional data in a very short period of time.
Although the recently developed 2D readers have many advantages over their one dimensional counterparts, they require additional electrical and lighting components, and thus occupy more space. Space in a hand-held reader is rather limited and any reduction in the size and weight of the optical unit adds greatly to the ease of operation of the reader and a corresponding reduction in operator fatigue. In addition, a small, light weight reader can be more easily and accurately placed upon a target thereby minimizing the amount of time the reader must be on, which is an important consideration with regard to battery operated units.
The 2D readers are usually equipped with light emitting diodes (LED) for illumination a target. The LEDs are arranged upon a board about the lens system which focuses an image of the illuminated target upon the 2D imager. The distal ends of the LEDs, however, extend some distance beyond the front lens of the lens system. In addition, these readers are equipped with light polarizing filters which are mounted in front of the LED. As a consequence, a good deal of space forward of the lens system is required to accommodate the LEDs and polarizing filters. Placing the LEDs forward of the lens system can also have an adverse effect on image quality, particularly when the target is mounted upon a highly reflective surface. Direct light from the LEDs can, under certain conditions, combine with the light coming back to the imager from the highly reflective surface to over-expose the imager.
If the illuminating structure of 2D readers are equipped with aiming devices, such as LEDs or laser diodes, additional space is required to position and mount these devices. In those readers in which LEDs are used to generate aiming illumination patterns, those patterns are often poorly defined unless special aiming optics assemblies are provided. In those readers in which laser diodes are used to generate aiming illumination patterns, these patterns are often well defined, but are costly to build, and consume substantial amounts of power.
One 2D reader having an illumination assembly that uses LEDs for both illumination and for aiming is shown and described in U.S. patent application Ser. No. 08/649,126, filed May 14, 1996, which is hereby expressly incorporated herein by reference to the extent that it is not reproduced herein. Another 2D reader of this type is shown and described in U.S. Pat. No. 5,521,366 (Wang et al).
2D readers having laser based aiming pattern illumination generators is described in U.S. Pat. Nos. 5,500,516 (Durbin) and 5,019,699 (Koenck). A 2D reader having a spotter beam is described in U.S. Pat. No. 5,541,419 (Arackellian).
Because of the above-mentioned deficiencies, a need has existed for an illuminating assembly that is compact, efficient in it use of electrical power and has the ability to generate a well defined aiming illumination pattern.